Abstract

Human physiological processes are complemented by those of the microbiota, the collection of all microbes living in and on our body. The human intestinal microbiota is one of the most prominent representatives and many associations with a wide spectrum of human diseases have been identified. Analysing faecal material with nucleic acid based approaches revealed the species richness of the intestinal microbiota and its individuality, being unique to each human being. In addition, to date approximately ten million unique genes have been identified from the human intestinal microbiota. These genes add an enormous additional genetic potential to the human genome, but little is known about which of these genes can be expressed into proteins and the conditions under which the protein synthesis occurs. The focus of this thesis work was to increase the knowledge of the biological processes taking place in-vivo, and to establish a baseline of these functions in the intestine of a healthy adult. Faecal material was used to study the metabolic reactions in the lower intestine, thus avoiding invasive sampling like biopsies. The proteins contained in the faecal material, which represent the molecules of most biological reactions, were targeted. At first, a method to access and analyse faecal proteins was developed, a so called metaproteomics approach. Proteins were analysed by mass spectrometry and the vast amount of resulting data was analysed with a wide range of computational methods to get a comprehensive overview of the intestinal functions. Altogether, 81 biological samples collected from 48 adults were analysed. As the main result, it was shown that individuals can be separated by their specific faecal protein profiles. This, in turn, indicates that the collection of intestinal microbial functions taking place in each of us are unique. In addition, the faecal protein profiles from obese individuals were found to be different from those of non-obese individuals. On a phylum level, it appeared that in obese individuals Bacteroidetes were biologically more active than the phylogenetic analysis suggested. This thesis work has identified several core intestinal proteins and helps to understand the functional significance of the intestinal microbiota. Next, we have to address these proteins in well concerted studies and still need to learn more about many of the encoded functions contained in the intestinal microbial genes. Suolistossamme elää monimuotoinen mikrobisto, joka toiminnoillaan täydentää ihmisen fysiologisia prosesseja. Suolistomikrobit osallistuvat muun muassa ruuansulatukseen, tuottavat vitamiineja ja säätelevät immuunijärjestelmän toimintaa. Teknologisen kehityksen myötä erilaisia mikrobipopulaatioita pystytään tutkimaan aiempaa kattavammin molekulaarisilla menetelmillä, jotka eivät vaadi bakteerien kasvattamista laboratoriossa. Metagenomiikka pyrkii DNA-sekvensoinnilla selvittämään kokonaisen ekosysteemin geenistön. Suolistomikrobiston metagenomitutkimukset ovat osoittaneet, että yksittäisen ihmisen…